Automatic focusing device

ABSTRACT

Based on a video signal from a CCD ( 3 ), an exposure evaluation value producing circuit ( 8 ) produces an exposure evaluation value for automatic exposure, a focus evaluation value producing circuit ( 9 ) produces a focus evaluation value for autofocus, a prescribed value is set as a threshold value if the aperture area of an iris detected by a diaphragm amount detecting circuit ( 11 ) is equal to or higher than a prescribed value, and a threshold value is set according to the aperture area of the iris if the area is equal to or smaller than the prescribed value. If a luminance signal is larger than the reference value, integration of the high frequency component of a region having a luminance level equal to or higher than the threshold value is excluded.

TECHNICAL FIELD

The present invention relates to autofocus apparatuses and moreparticularly, to an autofocus apparatus for use in a video camera or thelike.

BACKGROUND ART

In an autofocus apparatus used in a video camera or the like, the highfrequency component of a luminance signal is used as a focusingevaluation value and a focus is supposed to be obtained when theevaluation value is largest. There is a system such as an iris foradjusting the brightness of the entire picture plane according to thebrightness of the picture plane to avoid saturation of the brightness.If therefore the entire picture plane is bright, the luminancedifference between a high luminance object present in the picture planeand the picture plane is not large, and therefore the brightness of thehigh luminance object is adjusted to avoid saturation, so that anout-of-focus, unclear image will not be saturated in the whitedirection, and the evaluation value in focus is largest.

According to conventional art, when the entire picture plane is bright,the brightness and evaluation value of the entire picture plane areadjusted to avoid saturation using an iris or the like and a focus isobtained in the presence of a high luminance object, but when the entirepicture plane is dark, the iris is considerably opened if there is apartly high luminance object. This is because if the iris is stoppeddown for a partly high luminance object, the entire picture plane alsobecomes very dark and the resultant image would appear quitedisagreeable when compared to the object actually observed by a person.Then, the high luminance part being greatly different from the entirepicture plane in luminance is saturated in the direction of white, andtherefore the saturated region will be large when it is out of focus,and the contour will be large, which increases the high frequencycomponent and the evaluation value. In that state, the autofocusapparatus often stops operating as if a focus is obtained.

It is therefore a main object of the present invention to provide anautofocus apparatus which removes a high frequency component from theevaluation value of an image having a high luminance part, by excludingintegration of the high frequency component in an area having aluminance level equal to or higher than a prescribed value when theentire picture plane is dark and the iris is considerably opened.

DISCLOSURE OF INVENTION

The present invention is directed to an autofocus apparatus to adjust animage input to an imaging device into focus by controlling a lens unit,and includes a focus evaluation value detecting circuit for integratingthe high frequency component of a video signal for each of a pluralityof regions formed by dividing a picture plane to output the result as afocus evaluation value, a focus control circuit for performing afocusing operation by displacing the relative position of the lens tothe imaging device such that the focus evaluation value is maximized, aluminance level detecting circuit for detecting the luminance level ofeach region of the picture plane, an iris detecting circuit fordetecting the aperture degree of an iris, an excluding circuit forselectively excluding integration of the high frequency component of aregion by the focus evaluation value detecting circuit in response tothe detected luminance level of the region being equal to or higher thana prescribe threshold level, and a control circuit for controlling theexcluding circuit to exclude integration of a high frequency componentin a region having a luminance level detected by the focus evaluationdetecting circuit higher than a prescribed value when the detected irisdegree indicates an aperture degree equal to or higher than a prescribedvalue.

Therefore, according to the present invention, in response to a detectediris degree indicating a value equal to or higher than a prescribedvalue, integration of the high frequency component of a region having aluminance level equal to or higher than a prescribed value is excluded,so that a focus can be promptly obtained in response to a high luminancepart such as a spot light in a dark background where the iris isextremely stopped down, so the picture plane is very much dark but stillappears agreeable.

More preferably, in response to the aperture degree of the iris, thethreshold value of the luminance level to determine a region which isexcluded from integration is changed.

According to a more preferable embodiment, if the detected aperture areaof the iris is not less than a prescribed value, the prescribed value isused as the threshold value, and if the aperture area of the iris is notmore than the prescribed value, the threshold value is set based on theaperture area of the iris.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of the general configuration of one embodimentof the present invention;

FIG. 2 is a detailed block diagram of an exposure evaluation valueproducing circuit shown in FIG. 1;

FIG. 3 is a detailed block diagram of a focus evaluation value producingcircuit shown in FIG. 1;

FIG. 4 is a view showing divisional areas (n, m) for producing a focusevaluation value;

FIG. 5 is a view showing divisional areas (A1 to A6) for producing theexposure evaluation value of a picture plane;

FIG. 6 is a graph showing the focus evaluation value and thedisplacement of a lens;

FIG. 7 is a graph showing the relation between the aperture area of aniris and the brightness;

FIG. 8 is a graph showing the relation between a reference value and theaperture area of an iris;

FIG. 9 is a graph showing the relation between the reference value andthe aperture area of the iris;

FIG. 10 is a flow chart for use in illustration of the specificoperation of one embodiment according to the present invention; and

FIG. 11 is a flow chart for use in illustration of the operation ofreceiving a focus evaluation value shown in FIG. 10.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a block diagram of one embodiment of the present invention. InFIG. 1, a focus lens 1 is used to obtain a focus to a CCD 3 through aniris 2, and there is provided a zoom lens having amagnification-changing function on the object side of focus lens 1though not shown. Focus lens 1 advances/withdraws in the direction ofthe optical axis by a lens driving portion 15 including a mechanismportion and a motor.

The object image formed at CCD 3 through the above-mentioned focus lens1 is photoelectrically converted into a video signal, which is convertedinto a digital video signal by an A/D converter 4. The digital videosignal is color-separated into R, G and B signals by a color separationcircuit 5 for application to a signal processing circuit 7, an exposureevaluation value producing circuit 8 and a focus evaluation valueproducing circuit 9. The above-described CCD 3, A/D converter 4, colorseparation circuit 5, exposure evaluation value producing circuit 8 andfocus evaluation value producing circuit 9 are provided with timingsignals generated by a timing generation circuit 10. Signal processingcircuit 7 adds a synchronizing signal to the video signal.

Iris 2 is used to adjust the quantity of light in the picture plane, andfor example the aperture degree of iris 2 is detected by a diaphragmamount detecting circuit 11 using a Hall element. The detected output ofdiaphragm amount detecting circuit 11 is applied to a threshold valueproducing circuit 16, and a threshold value according to the aperturedegree of iris 2 is produced and applied to focus evaluation valueproducing circuit 9. More specifically, threshold value producingcircuit 16 sets a prescribed value as the threshold value if theaperture area of iris 2 is not less than the prescribed value, and setsa threshold value according to the aperture degree of iris 2 if theaperture area of iris 2 is not more than the prescribed value.

For exposure evaluation value producing circuit 8, used is for examplean automatic exposure adjusting device as disclosed by Japanese PatentLaying-Open No. 3-32175 as will be described in detail in connectionwith FIG. 2. More specifically, exposure evaluation value producingcircuit 8 divides the picture plane into 6 regions A1 to A6 as shown inFIG. 5 and produces the luminance evaluation value of each region,produces the luminance level of the entire picture plane for correctlyadjusting exposure, and the thus produced exposure evaluation values areapplied to an iris control circuit 13. Iris control circuit 13 controlsan iris driving portion 14 based on the applied exposure evaluationvalue, and iris driving portion 14 adjusts the aperture degree of iris2.

When focus evaluation value producing circuit 9 divides a picture planeinto regions (1, 1) to (n, m) as shown in FIG. 4 based on RGB signalsapplied from color separation circuit 5, it integrates the highfrequency component of a video signal for each region and produces afocus evaluation value, and the output signal is applied to a focuscontrol circuit 12. Focus control circuit 12 displaces focus lens 1 fromthe near point to the infinite point and vice versa, and stops drivingfocus lens 1 as a focus is obtained when the focus evaluation valueattains a maximum value as shown in FIG. 6. Regions (1, 1) to (n, m) canbe segmented to the number of pixels in CCD 3 at most. A focusingoperation is for example described in detail by Japanese PatentLaying-Open No. 3-258171.

If the detection of the aperture degree of iris 2 by diaphragm amountdetecting circuit 11 indicating a level equal to or higher than aprescribed value, focus evaluation value producing circuit 9 excludesintegration of a high frequency component having a luminance level equalto or higher than a prescribed level according to a threshold valuereceived from threshold value producing circuit 16.

FIG. 2 is a detailed block diagram of the exposure evaluation valueproducing circuit shown in FIG. 1. In FIG. 2, a region dividing circuit81 is provided with RGB signals from color separation circuit 5 shown inFIG. 1. Region dividing circuit 81 forms six regions A1 to A6 bydividing, and applies a region dividing signal to an integration circuit82. Integration circuit 82 though not shown includes a digitalintegration circuit formed by an A/D converter, an adder to add theoutput of this A/D converter and the output of a succeeding latchcircuit, and a latch circuit to latch the addition output. Thisintegration circuit 82 causes a memory 83 to store an integration valuefor one field of a low frequency component of a luminance signal in eachof regions A1 to A6. Memory 83 has its data updated for each field.

When integration for one field in one picture plane completes, theupdated new integration value of one field in each region held in memory83 is applied to a weighting circuit 84 and a normalizing circuit 85 asluminance evaluation values Y1 to Y6 for the respective regions.Normalizing circuit 85 divides the luminance evaluation values Y1 to Y6of the regions by the areas of regions S1 to S6, respectively andoutputs the resultant values per unit area of each region as normalizedluminance evaluation values V1 to V6 (V1=Y1/S1, V2=Y2/S2 . . . ) to apriority determining circuit 86.

Priority determining circuit 86 determines the priority of each regionbased on each normalized luminance evaluation value. More specifically,priority determining circuit 86 compares for example the normalizedluminance evaluation value of region A1 in the center of FIG. 5 and thenormalized luminance evaluation value of region A2 in the periphery, anddetermines the priority of each region such that as these normalizedluminance evaluation values come closer to each other, the priorities ofregions A1 and A2 are larger than the priorities of peripheral regionsA3 to A6. Weighting circuit 84 weights the priority of each region forpriority processing. A weighted mean circuit 87 divides the added upvalue of the regions output from weighting circuit 84 by the sum of eachpriority and the area to produce a weighted average value, and theweighted average value is compared to a target value previously storedin a target memory 89 by a comparator 88 and an exposure evaluationvalue is output.

FIG. 3 is a detailed block diagram of the focus evaluation valueproducing circuit shown in FIG. 1. In FIG. 3, a luminance signalcomponent from RGB signals output from color separation circuit 5 shownin FIG. 1 is input to a high-luminance portion cut circuit 91.High-luminance portion cut circuit 91 is provided with a threshold valuefrom threshold value producing circuit 16 in FIG. 1.

A timing detecting circuit 97 detects a timing signal from a videosignal for application to a gate control circuit 98. Gate controlcircuit 98 produces a gate control signal to gate each divisional region(1, 1) to (n, m) shown in FIG. 4 for application to high-luminanceportion cut circuit 91.

High-luminance portion cut circuit 91 includes a luminance leveldetecting circuit 911, a comparator 912, and gate circuits 913 and 914.Luminance level detecting circuit 911 detects the luminance level ofeach region of a picture plane from the luminance signal componentapplied through gate circuit 914 and applies the detected luminancelevel to comparator 912. Comparator 912 compares the luminance level ofeach region detected by luminance level detecting circuit 911 and thethreshold value, allows the luminance signal to be output by openinggate circuit 913 if the luminance level is smaller than the thresholdvalue, and prohibits the luminance signal from being output if theluminance level is larger than the threshold value, so that integrationof the high frequency component of the region is selectively excluded.

Therefore, high luminance portion cut circuit 91 outputs the luminancesignal component of a video signal output from color separation circuit5 as it is to a high-pass filter (HPF) 92 for a normal blight scenewhere iris 2 is not fully open. High-pass filter 92 removes a low-bandcomponent of the video signal for application to a detecting circuit 93.Detecting circuit 93 detects a high frequency component of the luminancesignal. The detection output is converted into a digital value by an A/Dconverting circuit 94 and applied to an integration circuit 96.Integration circuit 96 produces a focus evaluation value by integratingthe applied luminance signal of each region. The thus formed focusevaluation value producing circuit 9 constantly outputs a focusevaluation value for 1 field.

FIG. 4 is a view showing how the picture plane is divided to produce afocus evaluation value, FIG. 5 is a view showing how the picture planeis divided to produce an exposure evaluation value, FIG. 6 is a graphshowing the relation between the focus evaluation value and thedisplacement value of the lens, FIG. 7 is a graph showing the relationbetween the aperture area of an iris and the brightness, FIG. 8 showsthe relation between the exposure evaluation value and the brightness,and FIG. 9 shows the relation between the threshold value and theaperture area of the iris. FIG. 10 is a flow chart for use inillustration of the operation of one embodiment of the presentinvention, and FIG. 11 is a flow chart for use in illustration of theoperation of receiving the focus evaluation value shown in FIG. 10.

Operations of one embodiment of the present invention will be nowspecifically described. Focus evaluation value producing circuit 9produces a focus evaluation value signal for application to focuscontrol circuit 12 as described in conjunction with FIG. 3, and in step(herein after simply as “S”) S1, focus control circuit 12 responds tothe focus evaluation value signal to advance/withdraw focus lens 1 usinglens driving portion 15. Then, in S2, focus control circuit 12 receivesa focus evaluation value N for the next one picture plane.

The reception of focus evaluation value N is processed according to theflow chat in FIG. 11. More specifically, in order to produce theevaluation values of regions starting from the first region (1, 1) ofregions (1, 1) to (n, m) shown in FIG. 4 to the last region (n, m), itis determined in S11 whether or not the region is the last region (n,m), and if it is not the last region, threshold value producing circuit16 determines in S12 if the aperture area of iris 2 detected bydiaphragm amount detecting circuit 11 is not less than a prescribedvalue. If it is determined in S13 that the aperture area of iris 2 isnot less than the prescribed value, the prescribed value is set as athreshold value. Then, it is determined in S15 whether or not theluminance signal is larger than a threshold value.

If the luminance signal is larger than the threshold value, highluminance portion cut circuit 91 prohibits the luminance signal frombeing output and impedes the luminance signal from being integrated byintegration circuit 96. If the luminance signal is smaller than thethreshold value, high-luminance portion cut circuit 91 outputs thesignal without cutting the luminance signal. As a result, integrationcircuit 96 integrates the high frequency component of the region. Theinitial state shown in the flow chart in FIG. 11 is regained, and if theaperture area of iris 2 is not less than a prescribed value, thresholdvalue producing circuit 16 sets the prescribed value as a thresholdvalue, and if the aperture area of iris 2 is not more than theprescribed value in S14, the threshold value is set according to theaperture area of iris 2.

More specifically, as shown in FIG. 7, such a control is made that thebrighter the object is, the smaller will be the aperture area. As shownin FIG. 8, however, if the brightness is not more than a prescribedvalue, in other words, if the picture plane is dark, iris 2 is fullyopen and the quantity of light input to CCD 3 is determined based onlyon the brightness of the lens. Therefore, according to the embodiment,as shown in FIG. 8, until iris 2 is opened, threshold value a shown inFIG. 9 is set, and in a dark picture plane after the iris is opened, theprescribed value b in FIG. 9 is set as a threshold value.

When the evaluation values of regions (1, 1) to (n, m) are integrated,the evaluation value for one picture plane is output. Then back to theflow chart in FIG. 10, the focus evaluation value output in S2 isreceived, focus evaluation value N previously received in S3 is comparedto the present received focus evaluation value N+1, and if the presentfocus evaluation value N+1 is larger, the focus evaluation value isupdated to N+1 in S4. It is determined in S5 if focus lens 1 isdisplaced until the focus evaluation value is maximized, if notmaximized, the initial state is regained to displace focus lens 1, andthe series of operations are repeated.

Focus control circuit 12 shown in FIG. 1 applies a driving signal tolens driving portion 15 in response to a focus evaluation value signaloutput from focus evaluation value producing circuit 9, and lens drivingportion 15 drives focus lens 1.

When iris 2 is fully open in a dark picture plane, diaphragm detectingcircuit 11 detects the state, and applies a detection signal tothreshold value producing circuit 16 accordingly. Threshold valueproducing circuit 16 sets a threshold value for high luminance to be cutat high-luminance portion cut circuit 91 based on the detection outputfrom diaphragm amount detecting circuit 11. Thus, high-luminance portioncut circuit 91 cuts the high-luminance component above the thresholdvalue, and detecting circuit 93 detects only the high frequencycomponent not more than the cut high luminance signal component.Therefore, if an object having a high-luminance part in a generally darkbackground enters into a picture plane, the high luminance component isremoved as iris 2 is fully open, and the evaluation value will notincrease when a focus is not obtained and the image is blurry, so that afocus can be obtained for such a high luminance object withoutdifficulty. As a result, a high-luminance part in a dark background suchas a spot light when a generally much dark picture plane appearsagreeable, a focus can be obtained promptly without difficulty.

Industrial Applicability

As in the foregoing, an autofocus apparatus according to the presentinvention is suitable for use in a video camera adjusted using an irisor the like such that the brightness and evaluation value of the entirepicture plane are not saturated when the entire picture plane is bright.

What is claimed is:
 1. An autofocus apparatus controlling the positionof a lens to obtain a focus for an image input to an imaging devicethrough an iris comprising: focus evaluation value detecting means forintegrating a high frequency component of a video signal for each of aplurality of regions formed by dividing a picture plane to be imaged bysaid imaging device to output the result as a focus evaluation value; afocus controller controlling the relative position of said lens to saidimaging device to be changed, thereby obtaining a focus such that saidfocus evaluation value is maximized; a luminance level detectordetecting a luminance level of each of the regions of said pictureplane; an iris detector detecting the aperture degree of said iris; aregion excluding unit selevtively excluding integration of a highfrequency component of a region by said focus evaluation value detectorin response to the detected luminance level of the region being equal toor higher than a threshold value; and a region excluding controllercontrolling said region excluding unit to exclude integration of a highfrequency component of the region whose detected luminance level isequal to or higher than said threshold value in response to the aperturedegree of siad iris detected by said iris detector being at a levelequal to or higher than a prescribed value.
 2. The autofocus apparatusas recited in claim 1, wherein said region excluding controller changessaid threshold value of the luminance level to determine said region tobe excluded from integration in response to the aperture degree of theiris detected by said iris detector.
 3. The autofocus apparatus asrecited in claim 2, wherein said region excluding controller sets aconstant value corresponding to said prescribed value as said thresholdvalue if the aperture area of the iris detected by said iris detector isequal to or higher than said prescribed value and sets said thresholdvalue according to the aperture area of said iris if the aperture areaof said iris is equal to or smaller than said prescribed value.
 4. Anautofocus apparatus controlling the position of a lens to obtain a focusfor an imaging input device through an iris comprising the steps of:integrating a high frequency component of a video signal for each of aplurality of regions formed by dividing a picture plane to be imaged bysaid imaging device to output the result as a focus evaluation value;controlling the relative position of said lens to said imaging device tobe changed, thereby obtaining a focus such that said focus evaluationvalue is maximized; detecting a luminance level of each of the regionsof said picture plane; detecting the aperture degree of said iris;selectively excluding integration of a high frequency component of aregion by said focus evaluation value output step in response to thedetected luminance level of that region being equal to or higher than athreshold value; and controlling said region excluding step to excludeintegration of a high frequency component of the region whose detectedluminance level is equal to or higher than said threshold value inresponse to the aperture degree of said iris detected by said irisdetecting step being at a level equal to or higher than a prescribedvalue.
 5. The autofocus method as recited in claim 4, wherein saidcontrolling step changes said threshold value of the luminance level todetermine said region to be excluded from integration in response to theaperture degree of the iris detected by said iris detecting step.
 6. Theautofocus method as recited in claim 5, wherein said controlling stepsets a constant value corresponding to said prescribed value as saidthreshold value if the aperture area of the iris detected by said irisdetecting step is equal to or higher than said prescribed value and setssaid threshold value according to the aperture area of said iris if theaperture area of said iris is equal to or smaller than said prescribedvalue.